This invention relates to a process for producing a calcium carboxylate from a nitrile compound using calcium hydroxide or calcium oxide and water. In one aspect, this invention relates to a process for producing calcium propionate from propionitrile and calcium hydroxide or calcium oxide.
Calcium carboxylates produced according to the process of the invention can be used to produce the corresponding carboxylic acids. Calcium carboxylates also have other uses. For example, calcium acetate is used as a thickening agent, such as in cake batters, puddings, and pie fillings, as buffers in controlling pH of food during various stages of processing as well as in the finished product, as a preservative to prevent microbial growth, and as a calcium supplement in pet products. In addition, calcium propionate is used on a large scale as a preservative in the foodstuffs sector, particularly in baked goods to inhibit molds and other microorganisms, and as a preservative and nutritional supplement in animal feeds.
Calcium carboxylates are typically prepared by the conventional methods for synthesizing carboxylic acid salts, for example by reacting a carbonate, hydroxide, or oxide with a concentrated or dilute carboxylic acid. Calcium propionate is typically produced from propionic acid and calcium hydroxide.
U.S. Pat. No. 4,700,000 (Merkel et al.) discloses an improvement to the conventional process for producing calcium propionate from propionic acid. Merkel et al. discloses that water formed during the reaction of calcium hydroxide with propionic acid is removed as an azeotropic mixture of water and propionic acid. Merkel et al. discloses that the vaporous mixture of water and propionic acid advantageously used for the preparation of calcium propionate by a process whereby this mixture is passed into an aqueous mixture containing calcium propionate and calcium hydroxide, with or without propionic acid, during which the pH is adjusted to 5-10 by further addition of calcium hydroxide, and the calcium propionate is isolated by crystallization.
U.S. Pat. No. 3,876,691 (Lincoln) discloses the hydrolysis of nitrites with an aqueous solution of barium hydroxide to produce the barium salt of the carboxylic acid corresponding to the nitrile. Lincoln, however, discloses that calcium oxide was ineffective as the hydrolyzing agent and that barium hydroxide is unique in its ability to hydrolyze nitrites as compared with the other most common alkaline earth metal hydroxide, i.e. calcium hydroxide (see Example III of Lincoln).
U.S. Pat. No. 5,763,652 (Kawabe et al.) discloses the hydrolysis of a nitrile compound with a basic catalyst to form a salt of a carboxylic acid and a base, wherein the basic catalyst is particularly an alkali metal hydroxide (col. 3, lines 4-6). Kawabe et al. also discloses the hydration of a nitrile compound to the corresponding amide in the presence of a manganese oxide catalyst. Optionally, the hydration of the nitrile compound can be conducted in the presence of a combination of the manganese oxide and a metallic simple substance or compound containing Group Ia elements (e.g. Na, K, etc.), Group IIa elements (e.g. Mg, Ca, Ba, etc.), Group IIb elements (e.g. Zn), Group IVa elements (e.g. Zr, etc.), Group IVb elements (e.g. Sn, etc.), and Group Va elements (e.g. V, etc.). (See col. 12, lines 26-65). Kawabe et al. further discloses that the amide compound formed by the hydration of the nitrile compound can be hydrolyzed by an inorganic base, for example, alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogencarbonates, alkaline earth metal hydroxides, and alkali earth metal carbonates, preferably alkali metal hydroxides and carbonates (see col. 15, lines 47-57, and col. 16, lines 1-6). Kawabe et al. does not disclose the hydrolysis of a nitrile compound with calcium hydroxide nor the hydration of a nitrile compound with a calcium compound alone.
Therefore, to produce calcium propionate from propionitrile, one of ordinary skill in the art would first convert the propionitrile to the free acid via acid or caustic hydrolysis. The acid hydrolysis would produce large amounts of a byproduct ammonium salt. Typical base hydrolysis with caustic soda, i.e. sodium hydroxide, would consume large quantities of sodium hydroxide, or require capital-intensive electrodialysis to recover the sodium hydroxide. The acid would subsequently be reacted with calcium hydroxide or calcium oxide to produce calcium propionate. In the alternative, one of ordinary skill in the art, based on the teaching of the Kawabe et al. patent, would hydrate a nitrile compound using a manganese oxide catalyst to produce the corresponding amide and then hydrolyze the amide compound using a base, e.g. calcium hydroxide.
A commercially practical process for producing calcium carboxylates directly from nitrile compounds and a calcium compound has now been discovered.
According to the invention, a process for producing a calcium carboxylate is provided comprising contacting a nitrile compound, a calcium compound selected from calcium hydroxide, calcium oxide or mixtures thereof, and water at a temperature of about 90xc2x0 C. to about 250xc2x0 C. at a sufficient pressure and for a sufficient time to produce a reaction mixture comprising calcium carboxylate.
Further according to the invention, ammonia is removed from the reaction mixture and the calcium carboxylate is recovered.
Still further according to the invention, a process for producing a calcium carboxylate is provided comprising (a) contacting a nitrile compound, a calcium compound selected from calcium hydroxide, calcium oxide or mixtures thereof, and water in a reaction vessel at a temperature of about 90xc2x0 C. to about 250xc2x0 C. at a sufficient pressure and for a sufficient time to produce a first reaction mixture comprising calcium carboxylate, the amide corresponding to the nitrile compound, calcium hydroxide, water and ammonia; (b) venting the reaction vessel with or without prior cooling to remove ammonia and produce a second reaction mixture; (c) optionally adding additional water to the second reaction mixture; (d) heating the second reaction mixture to a suitable temperature to remove additional ammonia and, optionally, water from the second reaction mixture and hydrolyze at least a portion of the amide to produce additional calcium carboxylate; and (e) recovering the calcium carboxylate.